Insights into biological delignification of rice straw by Trametes hirsuta and Myrothecium roridum and comparison of saccharification yields with dilute acid pretreatment

Rice straw is the most abundant agricultural residue on a global scale and is widely available as feedstock for cellulosic fuel production. However, it is highly recalcitrant to biochemical deconstruction and also generates inhibitors that affect enzymatic saccharification. Rice straw from eastern Arkansas was subjected to dilute acid pretreatment (160 °C, 48 min and 1.0% sulfuric acid) and solid-state fermentation with two lignocellulolytic fungi, Trametes hirsuta and Myrothecium roridum, and their saccharification efficacies were compared. T. hirsuta and M. roridum were tested separately; pretreatment of rice straw with either strain for seven days resulted in 19 and 70% enrichment of its holocellulose content, respectively. However, liquid chromatography analysis of the alkali extracts showed significant differences in cell wall degradation by T. hirsuta and M. roridum. T. hirsuta removed 15% more phenolic compounds and 38% more glucan than M. roridum, while M. roridum removed 77% more xylan than T. hirsuta. Fungal and dilute acid pretreated biomass was then hydrolyzed using Accellerase^® 1500, a saccharification cocktail. Saccharification efficiency of M. roridum was 37% higher than that of dilute acid pretreatment of rice straw, requiring 8% lower enzyme loading and 50% shorter enzymatic hydrolysis duration. Alkali extraction of fungal pretreated biomass also yielded 10–15 g kg⁻¹ of acid precipitable polymeric lignin (APPL), which is a valuable co-product for biorefineries. In comparison to dilute acid pretreatment, fungal pretreatment could be a cost-effective alternative for the degradation of recalcitrant biomass, such as rice straw.     

双酶法制糖控制策略在DCS上的实现

目前制糖工艺流程基本是手动控制或半自动化控制，极少数企业采用DCS系统进行集中控制，特别是应用于“一线液化两线糖化”的制糖生产工艺流程中。从实际的生产应用中介绍“两次液化-两次加酶”法生产淀粉糖生产工艺、自动化控制系统的原理、JX-300 DCS系统简述、DCS系统构成和系统组态、系统调试，重点捕述“一线液化两线糖化系统”在DCS上的具体实现。通过近五年的运行，该系统控制方案是可行的，工艺运行稳定可靠，完全满足工艺的要求。     

Assessment of the structural factors controlling the enzymatic saccharification of rice straw cellulose

In this study, the structural factors controlling the enzymatic saccharification of rice straw cellulose were examined by preparing structure-modified rice straw samples such as dewaxed, alkali-treated, oxidized, and swollen rice straw. It was found that the initial enzymatic saccharification rate of the various structure-modified samples was largely controlled by the initial cellulose surface area of the cellulose unit. Although the presence of lignin limited the cellulose surface area, there was no strong relationship between the lignin content and the initial reaction. On the other hand, the long-term enzymatic saccharification of rice straw cellulose highly depended on the lignin removal rate (lignin content). It was also found that silica is not a crucial factor in controlling the enzymatic saccharification.     

Characterization of a β-1,4-glucosidase from a newly isolated strain of Pholiota adiposa and its application to the hydrolysis of biomass

The highly efficient β-1,4-glucosidase (BGL)-secreting strain, Pholiota adiposa SKU0714, was isolated and identified based on its morphological features and sequence analysis of internal transcribed spacer (ITS) rDNA. P. adiposa BGL (PaBGL), which contained a carbohydrate moiety, was purified to homogeneity from P. adiposa culture supernatants by 2-step chromatography on DEAE and Sephacryl gel filtration columns. The relative molecular weight of PaBGL was 60 kDa by SDS-PAGE or 59 kDa by size exclusion chromatography, indicating that the enzyme is a monomer. The pH and temperature optima for hydrolysis were 5.0 and 65 °C, respectively. PaBGL showed the highest activity towards p-nitrophenyl-β-d-glucopyranoside (V_max = 4390 U mg protein⁻¹, K_m = 2.23 mol m⁻³) and cellobiose (V_max = 3460 U mg protein⁻¹, K_m = 5.60 mol m⁻³) ever reported. Its internal amino acid sequences showed homology with hydrolases from the glycoside hydrolase family 3 (GH3), indicating that PaBGL is a member of the GH3 family. The hydrolysis of rice straw using a commercial cellulase, Celluclast^® 1.5L, resulted in a higher saccharification yield with the addition of PaBGL than with Novozyme 188. PaBGL may be a good candidate for applications that convert biomasses to biofuels and chemicals.     

甘蔗渣纤维表面Zeta电位变化特性及其对酶水解效果的影响

将纤维素原料降解为可发酵糖是木质纤维素生物质生物转化乙醇过程中的重要环节,通过对原料的预处理可以提高纤维素酶的催化效率.本文通过改变甘蔗渣纤维的尺寸、添加多聚磷酸盐等方法,发现均能改变蔗渣纤维的表面Zeta电位.初步研究了其Zeta电位变化规律及Zeta电位的变化对纤维素酶水解效果的影响,并对Zeta电位的变化影响纤维...     

超声波辅助淀粉双酶水解技术及其机理

为了探索超声波对淀粉液化和糖化酶解过程的影响及其机理,以液化值和葡萄糖当量值(DE)为指标,探讨了超声波功率、超声时间、淀粉乳浓度对淀粉酶解过程中还原糖产率的影响。结果表明:在超声功率100 W,超声时间10 min,淀粉乳浓度20%的条件下,淀粉乳的液化值及DE值从未处理样品的19.89mg/mL、82.06%分别提高到30.67 mg/mL、94.30%。超声波处理,使得淀粉颗粒表面的凹痕和裂痕明显增多,淀粉结晶结构遭到破坏,红外结晶指数下降,淀粉支链结构破坏,直链淀粉含量增加,溶解度提高了246.8%。此外,超声波处理对酶的激活作用使得α-淀粉酶活力提高了15.29%。     

Software for Simulation of Second‐Generation Ethanol Production by a Simultaneous Saccharification and Fermentation Process

Environmental impacts associated with the consumption of fossil fuels and the need to generate power through renewable resources demands the usage of alternative materials. The objective is the production of clean energy from materials like lignocellulosic biomass to produce second‐generation (2G) ethanol. A software in the Matlab program is elaborated to simulate the simultaneous saccharification and fermentation (SSF) process of lignocellulosic biomass for the 2G ethanol production in batch reactors. Studying the effects of the process variables, it was found that the higher interference is caused by cellulose concentration. Higher concentrations of the product in batch processes are obtained with the maximum cellulose concentrations, cells, and enzyme.     

Ethanol production from food residues

Food residues were converted to ethanol by simultaneous saccharification with an amylolytic enzyme complex (a mixture of amyloglucosidase, ??-amylase, and protease), and fermentation (SSF) with the yeast, Saccharomyces cerevisiae. About 36 g dm⁻³ of ethanol was obtained from 100 g dm⁻³ food residue in 48 h of fermentation. In the SSF with no nitrogen supplements, 25 g dm⁻³ of ethanol was produced from 100 g dm⁻³ food residues. In addition, none of the nutrient components except yeast extract from the SSF medium were found to affect ethanol production from food residues. This result indicates that food residues could be a good economic bioresource for ethanol production.     

Enhanced saccharification of SO2 catalyzed steam-exploded corn stover by polyethylene glycol addition

Corn stover is a renewable, low cost and abundant feedstock in China. Its effective utilization is crucial for providing bioenergy, releasing environmental pollution and increasing farmers’ income. This aim of this study was to obtain the efficient saccharification of SO₂ catalyzed steam-exploded corn stover (SSECS) by polyethylene glycol (PEG) addition. According to the results, adding PEG6000 could lower the enzyme loading by 33.3%. With 20% solid loading, the highest glucose concentration of 102 g L⁻¹ and 91.3% saccharification yield were obtained using 30 CBU (g glucan)⁻¹ ??-glucosidase and 10 FPU (g glucan)⁻¹ cellulase in presence of PEG6000. In addition, protein and enzyme activities assays in the supernatants revealed that PEG could facilitate the desorption of enzyme protein from lignocellulose. These indicated that PEG addition not only can enhance enzymatic saccharification at high substrate concentration, but also can improve enzyme recycling by reducing the enzyme activity loss caused by adsorption during the hydrolysis.     

Detoxification of woody hydrolyzates with activated carbon for bioconversion to ethanol by the thermophilic anaerobic bacterium Thermoanaerobacterium saccharolyticum

Autohydrolysis is a simple, green method of recovering sugars from biomass, using only hot water. One potential drawback is that byproducts are formed during the autohydrolysis process that could interfere with subsequent hydrolysis and fermentation to ethanol. In the present work, autohydrolysis prehydrolyzate from mixed hardwood chips was detoxified with activated carbon and the removal efficiency of byproducts as well as the loss of sugars determined. The resulting detoxified prehydrolyzate was evaluated for the fermentation to ethanol with a thermophilic anaerobic bacterium. Activated carbon at a 2.5 wt % level on the prehydrolyzate was able to remove 42% of formic acid, 14% of acetic acid, 96% of hydroxymethylfurfural (HMF) and 93% of the furfural. However, 8.9% of sugars were also removed. The removal of HMF and furfural follow expected adsorption isotherms but formic acid, acetic acid, and sugars did not. Autohydrolysis prehydrolyzates from mixed hardwood detoxified with activated carbon can be fermented with Thermoanaerobacterium saccharolyticum strain MO1442 with an essentially 100% yield. T. saccharolyticum strain MO1442 is able to metabolize the glucose, xylose, and arabinose in the hydrolyzate. The results showed the detoxification process with activated carbon improved the ethanol yields by the removal of toxic compounds, mainly HMF and furfural, with moderate loss of fermentable sugars.